The present invention relates to a liquid crystal display device (hereinafter, referred to as xe2x80x9cLCDxe2x80x9d), and particularly to an LCD with its upper and lower cases clamped together by crimping portions of one of the upper and lower cases at the other.
LCDs have been widely adopted as display devices capable of displaying a high-definition color image used for notebook computers and display monitors.
LCDs are of the following two types. One is a simple matrix type LCD which uses a liquid crystal panel having a liquid crystal layer sandwiched between a pair of substrates each having a plurality of electrodes parallel with each other on its inner surface with the electrodes on one of the pair of the substrates intersecting the electrodes on the other of the pair. The other is an active matrix type LCD which uses a liquid crystal panel having a switching element for selecting each of a plurality of picture elements on one of a pair of substrates sandwiching a liquid crystal layer therebetween.
The active matrix type LCD is further classified into two types: one is a so-called vertical electric field type LCD (commonly called a TN active matrix type LCD) using a liquid crystal panel in which electrodes for selecting picture elements are formed on each of a pair of upper and lower substrates; and the other is a so-called horizontal electric field type LCD (commonly called an in-plane switching (IPS) type LCD) using a liquid crystal panel in which electrodes for selecting picture elements are formed on only one of a pair of upper and lower substrates.
The liquid crystal panel of the former TN active matrix type LCD is configured such that liquid crystal molecules are aligned to twist by 90xc2x0 between a pair of substrates and a pair of polarizers are attached on the outer surfaces of the upper and lower substrates of the liquid crystal panel such that their absorption axes are in a cross-Nicol arrangement and the absorption axis of the entrance-side polarizer is parallel or perpendicular to a direction of rubbing a liquid crystal molecule alignment film adjacent to the entrance-side polarizer.
In such a TN active matrix type LCD, when no voltage is applied to the liquid crystal layer, incident light is linearly polarized through the entrance-side polarizer. The linearly polarized light propagates along the twisted liquid crystal molecules of the liquid crystal layer, and if the transmission axis of the exit-side polarizer conforms to the azimuthal angle of the linearly polarized light, the linearly polarized light entirely goes out of the exit-side polarizer to form a white image (so-called normally open mode).
When a voltage is applied to the liquid crystal layer, directors of unit vectors each indicating the mean alignment direction of the molecular axis of each of liquid crystal molecules of the liquid crystal layer are made perpendicular to the substrate plane, and they conform to the absorption axis of the exit-side polarizer because the azimuthal angle of the entrance-side linearly polarized light is not changed, thereby leading to a black image (see xe2x80x9cBasis and Application of Liquid Crystalxe2x80x9d published by Kougyo Chousa Kai in 1991).
On the other hand, for the IPS type LCD in which electrodes for selecting picture elements and electrode lines are formed on only one of a pair of substrates and the liquid crystal layer is switched in a plane parallel to the substrate by applying a voltage between two adjacent electrodes (a picture element electrode and a counter electrode) on the substrate, the polarizers are disposed so that a black image is formed when no voltage is applied to the liquid crystal layer (so-called normally close mode).
In the IPS type LCD, molecules of the liquid crystal layer are parallel to the substrate and in a homogeneous alignment. In the case where no voltage is applied to the liquid crystal layer, directors of the liquid crystal layer in a plane parallel to the substrate are parallel to the arrangement direction of the electrodes or inclined therefrom at a small angle. On the other hand, in the case where a voltage is applied to the liquid crystal layer, the direction of the directors of the liquid crystal layer is shifted in the direction perpendicular to the arrangement direction of the electrodes along with the applied voltage to the liquid crystal layer, and when the direction of the directors of the liquid crystal layer is inclined by 45xc2x0 toward the electrode lines with respect to the direction of the directors of the liquid crystal molecules in the case where no voltage is applied to the liquid crystal layer, the liquid crystal layer turns the azimuthal angle of the plane of vibration of the polarized light by 90xc2x0 like a half-wave plate. At this time, since the transmission axis of the exit-side polarizer conforms to the azimuthal angle of the plane of vibration of the polarized light, the polarized light going out of the exit-side polarizer forms a white image.
The IPS type LCD is advantageous in that the hue and contrast are less changed even if the viewing angle is changed, to increase an acceptable range of viewing angles (see Japanese Patent Laid-open No. Hei 5-505247).
A color-filter method is mainly used to manufacture the above-described LCDs of a full color type. In this method, a picture element equivalent to one dot of color display is divided into three parts, and three color filters equivalent to three primary colors, that is, red (R), green (G) and blue (B) are assigned to the above three divided parts of the picture element.
The present invention can be applied to the above-described various kinds of LCDs, and hereinafter, the present invention will be briefly described by example of the TN active matrix type LCD.
As described above, in a liquid crystal display element (also called liquid crystal panel) constituting part of the TN active matrix type LCD (hereinafter, referred to simply as xe2x80x9cactive matrix LCDxe2x80x9d), a plurality of gate lines extending in an X direction and arranged in a y direction, and drain lines insulated from the gate lines, extending in the y direction and arranged in the x direction are formed on the surface, on the liquid crystal layer side, of one of two transparent insulating substrates (made from glass or the like) oppositely disposed with a liquid crystal layer put therebetween.
Each of areas enclosed by these gate lines and drain lines constitutes a picture element area in which a thin film transistor (TFT) as a switching element and a transparent picture element electrode are formed.
When a scanning signal is supplied to the gate line, the thin film transistor is turned on, and in such a state, a video signal is supplied to the picture element electrode from the drain line via the thin film transistor thus turned on.
Not only the drain lines but also the gate lines extend to the periphery of the substrate to form external terminals, and a video driver circuit and a gate scanning driver circuit, that is, a plurality of driver ICs (semiconductor integrated circuits) constituting the video driver circuit and gate scanning driver circuit are mounted at the periphery of the substrate in such a manner as to be connected to the associated external terminals. That is to say, a plurality of tape carrier packages on each of which the driver ICs are mounted are mounted at the periphery of the substrate.
In such a substrate, however, since the TCPs on each of which the driver ICs are mounted are mounted at the periphery of the substrate, the area of a region (usually called a frame border) between the display area composed of intersections between the gate lines and drain lines of the substrate and the outer edges of the substrate becomes large, so that it becomes difficult to satisfy a requirement to reduce the outer size of the liquid crystal display module in which the liquid crystal display element is integrated with an illuminating light source (backlight) and other optical components.
To solve such a problem, that is, to satisfy the requirement against high density mounting of a liquid crystal display element and miniaturization of the outer shape of a liquid crystal display module, there has been proposed a so-called flip-chip method or chip-on-glass (COG) method in which video driver ICs and scanning driver ICs are directly mounted on a substrate without the use of the TCP parts.
A liquid crystal display device manufactured using the flip-chip method has been disclosed by the present applicant in Japanese Patent Laid-open No. Hei 6-256426.
The liquid crystal display device disclosed in the above document comprises: a liquid crystal display element (also called a liquid crystal display panel or a liquid crystal panel) comprising a pair of substrates made of glass or the like fixed to one another with a desired spacing therebetween by a sealing material disposed in a form of a frame in the vicinity of the edges of the substrates, transparent electrodes for displaying and liquid crystal molecule alignment films coated on the opposing inner surfaces of the substrates, liquid crystal material injected into a space enclosed by the substrates and the sealing material via an opening provided in the sealing material, and a pair of polarizers attached on the outer surfaces of the substrates; a backlight, disposed on the rear surface of the liquid crystal display element, for supplying light to the liquid crystal display element; a liquid crystal driver circuit board disposed around the outer edges of the liquid crystal display element; a molded lower case for housing and holding the backlight; and a metal shield case (also called an upper case or upper frame), having a display window, for housing the above components.
The backlight comprises an approximately rectangular light guide, formed of a synthetic resin plate, for example, a transparent acrylic resin plate, for directing the light from the light source away from the light source and uniformly illuminating the entire liquid crystal display element from the rear surface thereof with the light; a line light source (a fluorescent lamp such as a cold cathode fluorescent lamp) disposed in the vicinity of at least one end surface (one side surface) of the light guide in such a manner as to extend in parallel to the end surface of the light guide; a light reflector, formed into an approximately U-shape in cross-section and having an inner surface taken as a reflection surface, for covering the fluorescent lamp substantially over the overall length thereof; a light-diffusing sheet disposed on the light guide, having an upper surface taken as a prismatic surface formed by a large number of long prisms having a triangular cross section and arranged parallel with each other and having a lower surface taken as a smoothing surface, for controlling the angles at which the light from the backlight and which are otherwise varied in a wide range, within a specified range and diffusing the light emerged from the light guide; a prismatic sheet for improving the luminance of the backlight; and a reflecting sheet, disposed under the light guide, for reflecting the light emerged from the light guide toward the liquid crystal display element.
In the prior art LCD, a flexible circuit board provided at a peripheral portion on the rear surface of the liquid crystal display element is electrically connected to an upper case as a metal frame by soldering, with a spring metal piece interposed between the inner surface of the upper case and the circuit board.
However, with the advance of the reduction of the frame border area, there occurs a problem that it is difficult to carry out the soldering using such a metal piece, particularly, for the flexible circuit board for drain drive.
According to the prior art LCD, to suppress the positional offset between the liquid crystal display element and light guide and ensure the resistance to shock, the light guide is elastically fixed to the liquid crystal display element with a rubber cushion interposed therebetween. With this configuration, however, there occur problems that foreign matters may permeate between the liquid crystal display element and light guide (display area), and that since the width of the rubber cushion becomes narrower with the advance of the reduction of the frame boarder area, it is difficult to assemble the light guide with the liquid crystal display element.
The upper case and the lower case are clamped by crimping a plurality of crimping nails formed at the bottom edges of the sidewalls of the upper case, at the rear surface of the lower case.
These crimping nails are formed by making long narrow cuts in parallel with the underside of the lower case, in the bottom portions of the side walls of the upper case, and the upper and lower cases are clamped by crimping the nails at the underside of the lower case.
There has been a problem with this structure in that reliability of clamping of the upper and lower cases is degraded because of insufficient friction between the crimping nails and the underside of the lower case due to a small contact area of the crimping nails with the underside of the lower case.
An object of the present invention is to solve the above-described problems of the prior art and to provide a liquid crystal display device capable of easily realizing the reduction of the frame border area.
For achieving the aforesaid object, a liquid crystal display device according to an embodiment of the present invention includes a liquid crystal display element having a liquid crystal layer sandwiched between a pair of upper and lower substrates, a flexible circuit board disposed around a periphery of the liquid crystal display element, an illuminating light source including a line light source, a light guide and a reflector and disposed behind the liquid crystal display element, an upper case made of metal, having a sidewall bent back from a periphery of a front portion thereof and a window corresponding to a useful display area of the liquid crystal display element, a lower case made of resin for housing the illuminating light source, the upper case and the lower case being clamped by crimping a plurality of nails formed in the sidewall of the upper case at an outer surface of the lower case after stacking the liquid crystal display element, the flexible circuit board and the illuminating light source between the upper case and the lower case, wherein an electrical connection between the upper case and a grounding pattern formed on the flexible circuit board is made by at least one component in chip form having a conductive region and being attached to a portion of the grounding pattern bent over the lower substrate, and a metal tape having one end thereof being interposed between opposing portions of the upper and lower cases which are pressed against each other and the other end thereof being positioned to be pressed against the conductive region of the at least one component in chip form.
With this configuration, it is possible to reduce the cost by use of an easy-to-get small-sized chip component, and it is easy to electrically connect the grounding pattern of a flexible circuit board to the upper frame even if the width of the flexible circuit board becomes narrower along with the reduction of the frame border area.
For achieving the aforesaid object, a liquid crystal display device according to another embodiment of the present invention includes a liquid crystal display element having a liquid crystal layer sandwiched between a pair of upper and lower substrates, a flexible circuit board disposed around a periphery of the liquid crystal display element, an illuminating light source including a line light source, a light guide and a reflector and disposed behind the liquid crystal display element, an upper case made of metal, having a sidewall bent back from a periphery of a front portion thereof and a window corresponding to a useful display area of the liquid crystal display element, a lower case made of resin for housing the illuminating light source, the upper case and said lower case being clamped by crimping a plurality of nails formed in the sidewall of the upper case at an outer surface of the lower case after stacking the liquid crystal display element, the flexible circuit board and the illuminating light source between the upper case and the lower case, wherein the light guide and the liquid crystal display element are pressed against each other, and a rubber cushion is disposed between the light guide and peripheral portions of the lower case at least in the vicinity of portions where the upper case and the lower case are clamped by crimping the plurality of nails.
With this configuration, it is possible to prevent permeation of foreign matters between the liquid crystal display element and light guide, and to improve the resistance to shock of the liquid crystal display device.
For achieving the aforesaid object, a liquid crystal display device according to another embodiment of the present invention includes a liquid crystal display element having a liquid crystal layer sandwiched between a pair of upper and lower substrates, a flexible circuit board disposed around a periphery of the liquid crystal display element, an illuminating light source including a line light source, a light guide and a reflector and disposed behind the liquid crystal display element, an upper case made of metal, having a sidewall bent back from a periphery of a front portion thereof and a window corresponding to a useful display area of the liquid crystal display element, a lower case made of resin for housing the illuminating light source, the upper case and the lower case being clamped by crimping a plurality of nails formed in the sidewall of the upper case at an outer surface of the lower case after stacking the liquid crystal display element, the flexible circuit board and the illuminating light source between the upper case and the lower case, wherein the plurality of nails are formed such that the plurality of nails are crimped in a plane parallel with an underside of the lower case and have at least one bend before crimping in cross section parallel to the plane.
With this configuration, it is possible to enlarge the contact area between the crimping nails and the lower case, and hence to improve the reliability of crimp-clamping. In addition, the nail may be bent into various shapes such as a single-stepped shape, multi-stepped shape or a curved shape.